These appliances generate large amounts of water vapour which forms as condensation on any surface which is below the ‘dew point’. The dew point is the temperature at which air that is saturated releases excess moisture vapour.

The most exposed parts of a building can let in water if not properly maintained. Chimneys, roofs and parapets are particularly troublesome; water can seep through defective mortar fillets, lead flashings, and hips and ridges in roof junctions, and leaks can occur from badly maintained rainwater fittings. Leaks from parapets and valley gutters can result in serious damage to structural roof timbers. In addition, if mortar, rather than lime has been used to repair small cracks in pointing and render, moisture can seep through to the internal structure of the property.

Spillages within the home can also result in damp. These include burst and leaking pipes, and leaks from baths, showers, washing machines and dishwashers.

Rising damp is damp that comes from below ground. Floors can become damp if moisture cannot evaporate due to rubber-backed carpets or vinyl sheets. Concrete floors can also result in excess moisture being driven to walls and chimney stacks.

In general, properties built before the mid nineteenth century need to breathe, as unlike modern buildings that keep water out via a barrier system, they are constructed of absorbent materials that allow excess moisture to evaporate. Open fires drew in an abundance of air from loose fitting windows and doors resulting in a high degree of ventilation. It’s important to take this into consideration when renovating an old property.